1. Field of the Invention
The present invention relates to a disc cam type recirocative compressor for use in an air conditioning system for a vehicle. In particular, it relates to an improvement for restricting the rolling motion of the piston during operation in the vicinity of the upper and lower dead points of the stroke of the piston provided in the compressor of the above type, which compressor comprises a disc cam having an operating surface formed in a sinuous shape on each side thereof and a double headed piston, a cam roller being arranged between the cam and the piston while in sliding contact therewith, so that one rotation of the disc cam is transmitted to the piston through the contact with the cam roller to cause two reciprocations of the piston, whereby a compression of the operating fluid can be realized.
2. Description of the Related Arts
A disc cam type compressor, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 57-110783 and Utility Model Publication (Kokai) No. 57-114184, has a structure typically illustrated in FIGS. 1, 10, 11, and 12, in which a plurality of pairs of oppositely arranged front and rear cylinder bores 4 are provided through the interior of a cylinder block 16 with a cam chamber 5 intervening between each pair of the bores 4. The respective pairs of bores 4 are arranged in parallel to a drive shaft 3 and equiangularly to each other in the transverse cross-section of the cylinder block 16. A disc cam 13 having sinuously curved front and rear surfaces 13' is fixedly secured on the drive shaft 3 so as to rotate within the cam chamber 5 with the rotation of the drive shaft 3. In the respective pair of bores 4, a double headed piston 8 is slidably inserted so as to be movable in the forward and rearward directions. The piston 8 has a recess 15 in the inner walls opposite to the cam surface respectively for accommodating a cam roller 14F or 14R, whereby the piston 8 can be smoothly and reciprocatedly driven in the forward and rearward directions through the slidable and rotatable nip of the cam rollers 14F and 14R in accordance with the rotation of the disc cam 13. In this prior art compressor, axes c of rotation of a pair of the associated cam rollers 14F and 14R are transverse to a longitudinal axis b of the piston 8.
According to the above nipping mechanism of the cam rollers 14F and 14R for the disc cam 13, a serious problem of a rolling motion of the piston 8 during operation arises in the vicinity of the upper and lower dead points of the stroke of the piston 8. That is, the piston 8 is liable to move transversely toward the periphery of the disc cam 13 in an undesirable manner at these dead points, which, in turn, results in an abnormal noise. More specifically, when the piston 8 is moving from one dead point (for example, the lower dead point) to the other dead point (for example, the upper dead point) as shown in FIG. 12, contact points i, i of the cam rollers 14F, 14R against the disc cam 13 exist in areas opposite to each other relative to a plane including the longitudinal axis b of the piston 8 and that of the disc cam 13, while nipping the disc cam 13 between both cam rollers 14F and 14R. According to this well-balanced arrangement of the contact points, the rolling motion (in the up-down direction in FIG. 12) of the piston 8 can be restricted by either of the cam rollers 14F or 14R during the middle phase of the stroke of the piston 8. However, when the piston 8 has reached the dead point, as shown in FIG. 11, both the contact points i, i of the cam rollers 14F, 14R are positioned on the longitudinal axis b of the piston 8. This means that the action of the cam rollers 14F, 14R for restricting the up-down movement of the piston 8 is cancelled. Thus, the rolling motion of the piston 8 is liable to occur, especially during high speed operation, and in this case, a bridge portion 8' of the piston 8 touches the outer periphery of the disc cam 13 to generate noise.